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Originally Posted by TurnAround
This is a fun little problem isn't it. Cool.
Here's what I think it is; The wheel sensor works just like a bicycle speedo computer works. You can mount the sensor to the bike frame anywhere up and down the radius of the wheel. You then mount a small magnet on the the wheel's spoke and line it up with the sensor on the frame so the magnet passes by it. It is irrelevant where you mount the sensor along the radius of the circle because it takes the same amount of time for the magnet to fly by regardless of where it is.
Close in to the hub, it flys by slowly. Far out, it flys by very fast. But the TIME it took to fly by is exactly the same. To calculate speed from this you need an equation that also feeds off of the wheel diameter. Once you have that, you have the speed at all times... with "magnet fly by TIME" being the only variable in the equation.
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What you are referring to as 'fly by time' is not quite right. The time does vary with wheel speed, as the sensor is moving faster. However, the sensor is simply emitting a pulse, and the computer is counting pulses. Integrated over time, ie counting pulses in a given time, you get pulses/second. You are correct that there is a calculation in the computer to convert pulses (which are a constant per one wheel revolution) to a distance, as all the optional tires have the same rolling circumference. Yes, this is the same as a bicycle computer in concept.
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